In a symbolic warning about how close the world stands to suffering a nuclear catastrophe, the Bulletin of Atomic Scientists has moved the Doomsday Clock closer to midnight. The existential threat now poses a greater danger to humanity than at any time since the height of the Cold War. The standoff between Russia the US, the world’s biggest nuclear powers, as well as regional conflicts and the threat of terrorists getting their hands on nuclear material, can all lead to disastrous consequences. With global politics growing more unstable, are nuclear arms still the strongest deterrent to global war, or are they the biggest menace to the security of the world? And, with a new president in the White House, how will America’s nuclear arms policy evolve? We ask former US Secretary of Defense Dr. William Perry.